Optimization of wind farm portfolios for minimizing overall power fluctuations at selective frequencies: a case study of the Faroe Islands

Turið Poulsen, Bárður A. Niclasen, Gregor Giebel, Hans-Georg Beyer

Research output: Contribution to journalArticlepeer-review


Hourly modeled wind turbine power output time series – modeled based on outputs from the
mesoscale numerical weather prediction system Weather Research and Forecasting Model (WRF) – are used to
examine the spatial smoothing of various wind farm portfolios located on a complex isolated island group with
a surface area of 1400 km2. Power spectral densities (PSDs), hourly step-change functions, and duration curves
are generated, and the 5th and 95th percentiles and the standard deviations of the hourly step-change functions
are calculated. The spatial smoothing is identified from smaller high-frequency PSD amplitudes, lower hourly
fluctuations, and more flat duration curves per installed wind power capacity, compared with single wind turbine
outputs. A discussion on the limitation of the spatial smoothing for the region is included, where a smoothing
effect is observed for periods of up to 1–2 d, although it is most evident at higher frequencies. By maximiz-
ing the smoothing effect, optimal wind farm portfolios are presented with the intention of minimizing overall
wind power fluctuations. The focus is mainly on the smoothing effect on the 1–3 h timescale, during which the
coherency between wind farm power outputs is expected to be dependent on how the regional weather travels
between local sites, thereby making optimizations of wind farm portfolios relevant – in contrast to a focus on
either lower or higher frequencies on the scale of days or minutes, respectively, during which wind farm power
output time series are expected to be either close to fully coherent due to the same weather conditions covering a
small region or not coherent as the turbulences in separate wind farm locations are expected to be uncorrelated.
Results show that an optimization of the wind farm capacities at 14 pre-defined wind farm site locations has a
minimal improvement on the hourly fluctuations compared with a portfolio with equally weighted wind farm
capacities. However, choosing optimized combinations of individual wind farm site locations decreases the 1–
3 h fluctuations considerably. For example, selecting a portfolio with four wind farms (out of the 14 pre-defined
wind farm site locations) results in 15 % lower 5th and 95th percentiles of the hourly step-change function when
choosing optimal wind farm combinations compared with choosing the worst wind farm combinations. For an
optimized wind farm portfolio of seven wind farms, this number is 13 %. Optimized wind farm portfolios consist
of distant wind farms, while the worst portfolios consist of clustered wind farms.
Original languageEnglish
Pages (from-to)2335–2350
Number of pages16
JournalWind Energy Science
Publication statusPublished - 1 Dec 2022


  • wind energy
  • wind farm siting


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